These experiments are designed to compare several features of reach-to- grasp movements in normal subjects and cerebellar patients in order to obtain insights into the role of the cerebellum in regulating this well- organized, highly integrated behavior. The general hypotheses to be tested are that the cerebellum contributes significantly to the consistent, stereotypic relationship between wrist transport and grip aperture, that this structure is necessary to maintain this consistent pattern once it is established, that it is required for optimizing the acquisition and performance of pre-planned reach-to-grasp movements directed toward moving targets, and that it is essential for acquiring adaptive strategies necessary for making on-line corrections for perturbations of these movements once initiated. The experiments are based on a series of preliminary studies in human subjects as well as insights obtained from related experiments from the PI's laboratory that employed animal models of cerebellar dysfunction. Five specific projects will be undertaken. The first will characterize the organizational features of the reach-to-grasp movement that are modified as a consequence of cerebellar pathology. The second project will explore the relationship between cerebellar dysfunction and the integration of visual cues during two phases of the reach, the early transport phase before the grip is formulated and the later grip phase occurring as the target is approached. The third study will evaluate the capacity of cerebellar patients to respond to two different types of predictable changes in target position, one a step change in position and the second a change in position that is continuously proportional to the subjects' wrist velocity during the reach. The fourth experiment will assess the capacity of cerebellar patients to improve their performance when these same types of changes in target position are presented in successive trials. In the fifth project, the capacity of cerebellar patients to acquire adaptive strategies to elastic load perturbations applied during the transport and grip phases of the reach- to-grasp movement will be explored. In addition to testing specific hypotheses underlying the design of these experiments, the data will lend insights into general concepts regarding the cerebellum's role in regulating the acquisition and performance of goal-directed limb movements and also will contribute to the understanding of the motor abnormalities observed in cerebellar patients.